Imaging of fusion reaction zone in plasma focus

Abstract

In a low energy (2.3 kJ) Mather-type deuterium plasma focus, neutron and charged particle emission is investigated by using time-resolved neutron detectors and time-integrated charged particle pinhole imaging camera. The time-integrated charged particle pinhole images demonstrate the varying influence of magnetohydrodynamic (MHD) instabilities vis-a-vis filling pressure. The neutron production mechanism at play strongly depends upon the pressure. At lower pressure, the plasma column is highly unstable due to MHD instabilities and the neutron emission is found to be low with fluence anisotropy exceeding 3.5. At optimum pressure (2.5 mbar for this system), an almost stable dense plasma of about 17 mm3 volume is formed about 5 mm away from the anode, with neutron emission at its highest and the fluence anisotropy lowest. At higher pressure, the plasma column is stable, although it moves away from the anode like a jet and may then be called a moving boiler. In this case, the neutron emission is lowered compared to its optimum value and fluence anisotropy is increased. The data suggest beam-target mechanism at low pressure, trapped gyrating particles at optimum pressure and a jetlike moving boiler at higher pressure.